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well Darla got her new sofa this week and it turns out there is no room for my grow chamber that i was going to build. we have been half joking around for the last 18 months about building a greenhouse off the southside of the house. well guess what my project is for next spring/summer? basically the plan is to use the same principle of the local commercial greenhouse and use 2 layers of plastic. im looking more for practicality and cost effectiveness than for assetics. they have to replace their plastic about every 4 years which works for me. it gets quite cold here in the winter and i was thinking of a wood stove with an electric heater on a thermostat as back up. it just requires a few weekends during the summer cutting wood for fuel for the winter. for cooling in the summer i would use swamp coolers. the north side of the greenhouse will actually be the side of the house. the back sliding glass door will open up into the greenhouse with a door for access to the outside probably on the west wall which along with the east will be made of 2x4's and plywood and will be insulated and will have a couple glass windows. any flaws? humidity may be a problem with the wood stove but what suggestions are there to increase humidity? will spraying the floor of the greenhouse a few times a day keep the humidity up. i havent officially measured anything but it will be about 10 or 11 ft high. 20-25 ft long and about 10 ft wide. im a so so carpenter BUT i have an uncle and my sisters boyfriend are two of the best i have ever seen so i will have help. any thoughts?

You're in Montana? Right? How are you planning to distribute the heat inside the greenhouse so there are no cold spots that will kill your plants?

From your description I picture a room addition to your home with a few windows in it to put plants in front of, not a greenhouse. A greenhouse is a building or add-on room with nearly all of the walls glazed with some form of light-transmissive covering.

Here is a link to a site that will help you to calculate how much heat is needed to heat the greenhouse: Greenhouse heat calculator

excellent websites, thank you. i figured circulating fans should prevent cold spots. i really dont know how best to describe it. ill try again. our house is sitting east to west. the greenhouse's north wall will actually be the southside of the house. the east and west walls of the greenhouse will be made like regular walls of a house with a door on one of them, a couple windows on each end that can be opened during warm weather for freash air. the roof and south wall will be a double layer of film plastic supported by a frame. the house should beable to protect it from the worst of the cold winter winds. a good wood stove with circulaing fans to warm it with a real good electric heater to act as back up should i have to skip town. normally ill have someone to stop by the house, usually my mom or brother, when im out of town to take care of my animals but yah never know.

I realize Winter temperature is a concern and heating bills along with it but I would not make the East and West walls like a normal building. The plants will not get enough light with just a transparent roof. You also really need some automatic heating method. A wood stove will not put out enough heat I don't think and will require running 24hrs a day 7 days a week for weeks on end during the Winter. Are you sure you want to wake up every few hours during this time to load wood? If the stove goes out it will only be a matter of 30min or so before everything in the greenhouse freezes. You would be much better off looking into propane space heaters or an oil furnace or something.
If you bought a small hoop style frame it would cost you significantly less in construction costs vs 2x4 walls and trusses. You could use the money saved here for the heating and cooling systems.

I suggest reading some of the other threads on greenhouse building. Most recently the one by whispersiren on greenhouse lighting.
Tony

actually i dont think the east west walls being made of 2x4 walls will be too much of a problem. the house isnt sitting perfectly east-west it just made it easier for the description. the southside wall is actually more south west. also being that this isnt just for my CPs i do have orchids and such that need lower light levels. as to the heating issue. our house is heated by propane and i should be able to tap into it quite easily as the hot water heater is along the very wall im going to build against. im still may consider putting a wood stove in to help cut heating costs. you figure im home most weekends in the winter and such. it should help put a dent in the heating costs being that i can prolly pick up a decent used one for next to nothing. how much ventilation issue is there with propane space heaters? i had to deal with a kerosene one at work this last winter after the basement flooded and took out the furnace. its something i would rather not deal with again it was quite stinky even when kept well ventilated. ill read the other threads over this week and ask any more questions that i come up with.

Well the way I interpret your plans.. the side walls will be solid with the roof transparent? If the width is 10' and the walls are 8' tall.. the plants will only actually receive light for a a few hours. The rest of the day it will not be bright enough for most orchids and almost all cps. The walls need to be transparent from at least 3' off the ground to the top of the wall. If you have the funds you could use the double wall polycarbonate sheets on the outside and then the 2 layer inflated polyvinyl over that.

As for the woodstove.. go for it as a secondary source to cut your heating expense. I would deffinately go with the propane space heater as well. They are vented with single wall flue pipe with a double wall insulated thimble where it goes through the structure to the outside. I would size the heater as if the woodstove was not part of the equation. The links Joseph posted on heater sizing will give you a good idea how many btu's it will take.

A properly installed propane space heater will not vent ANY fumes into the greenhouse. So you shouldn't smell anything. Outside you might smell a little of that burned propane smell which you probably are familiar with having the propane furnace.

During the Summer you will need some sort of venting/cooling system. The link I posted in the other thread I mentioned has good information on various types of these. The simplest would be just some exhaust fans on one end with shutters on the other.. and a fogger system to maintain humidity and provide some cooling. This setup uses a fair amount of water though. More complicated but providing better cooling are the evaporative pad type systems. A small fogger system might be needed with these just to touch up the humidity periodically.

the south wall will also be transparent except for 2 or 3 ft at ground level. for cooling in the summer i was going to use a compination venting and evaporative pad setup. im in the research stage at the moment. ill check out the other threads and find the links you have posted before. thanks for the input.